1. Field of the Invention
This invention relates to an ink jet type recording head of an on-demand system which jets ink droplets in response to printing signals to form dots on a recording medium.
2. Description of the Prior Art
An ink jet type recording head comprises a flow passage unit and a displacement effecting unit. The flow passage unit comprises: a nozzle plate having nozzle openings; a flow passage forming substrate having pressure generating chambers which are communicated with the nozzle openings, a common ink chamber and ink supply inlets; and a vibrating member which sealingly covers the flow passage forming substrate, and which inflates and deflates the pressure generating chambers, being externally displaced. The displacement effecting unit is adapted to apply mechanical energy to the pressure generating chambers through the vibrating member to jet ink.
In the ink jet type recording head, each of the ink supply inlets greatly affect the picture quality of the resultant print as well as each of the nozzle openings, and is an important element which changes the flow passage impedance ratio of the ink supply inlet and the nozzle opening, and the absolute value of the flow passage impedance. Hence, the dimensions and the flow resistances of the ink supply inlet and the nozzle opening greatly affect various characteristics of the recording head such as an ink-droplet jetting speed, a quantity of ink droplet, and an ink-droplet jetting frequency.
This problem may be solved by a technique which has been disclosed, for instance, by Japanese Patent Application No. Hei. 5-229114. That is, by anisotropic-etching a silicon monocrystal wafer, the pressure generating chambers, the common ink chamber, and the ink supply inlets of the flow passage substrate can be formed with high dimensional accuracy.
On the other hand, in a recording head for high-density printing, the pressure generating chambers are large in aspect ratio, and walls 45 (FIG. 7) separating the pressure generating chambers from one another are thin, so that the bonding areas for bonding the nozzle plate and the vibrating member to the flow passage forming substrate are extremely small.
In an example of the conventional recording head described above, as shown in FIG. 7, a bonding region 41 on the side of the nozzle openings 40 is large, 800 .mu.m.times.141 .mu.m, while bonding regions around ink supply inlets 43, which are formed on one side of the flow passage forming substrate which is opposite to the other side where the pressure generating chambers 42 are formed, are each small, 25 .mu.m.times.200 .mu.m. The sum of those small bonding regions 44 around the ink supply inlets is also extremely small, about one-twentieth (1/20) of the bonding region 41 provided near the nozzle openings 40, and therefore it is difficult to obtain a sufficient adhesive strength on the side of the ink supply inlets.
Accordingly, at the junctions of the flow passage forming substrate, the nozzle plate and the vibrating member which form the ink flow paths, those components may be separated from one another for instance because of the non-uniform application of the adhesive agent; and the ink may leak from one of the pressure generating chambers into another. Thus, the conventional recording head is low in reliability.